The present invention relates to photodetectors. In particular, the present invention relates to a photodetector device for determining the wavelength of incident radiation from an unknown line (or "narrow band") source in a broad spectral range, or for distinguishing different blackbody or other broad band radiation sources.
Multicolor photodetector devices have been used in the past for spectral band analysis. For example, a radiometer which detects two wavelengths from the same braodband source and measures the ratio of the intensity of the two wavelengths can make temperature measurement independent of the emissivity of the source and the transmission of the intervening space. Examples of these devices are shown in U.S. Pat. No. 3,454,769 by Dynes, U.S. Pat. No. 3,478,214 by Dillman, and U.S. Pat. No. 3,638,026 by Scott et al and in H. Halpert and B. L. Musicant, "N-Color (Hg,CD)Te Photodetectors", Applied Optics, 11, 2157, (1972).
In general, these prior art devices utilize photodetectors of different band gaps. In most of the devices, narrow band filters are used to restrict the incident radiation to two narrow bands in the case of a two-color detector, or N narrow bands in the case of an N-color detector.
Although these devices can effectively distinguish different blackbody or other broad band radiation sources, they are unable to determine the wavelength of an unknown line source such as a laser.